Concrete roadway.



A E. M. CHADBOURNE.

CONCRETE ROADWAY. APPLICATION FILED MAR. 17, 1911;

Patefited May 30, 1911 1 QWQ EDWARD M, CHADBCURNE, 0F Sail? FRANClSCO, CALIFORNIA.

concnmn ROADWAY.

corona.

To all :whom it mag concern:

Be itknown that, 1", Eire-Ami M. CHAD- nonnrm, a citizen of the United States, re-

Specificaticn of Letters Patent. Application filed March 17, ran.

siding at San Francisco, in the county of San Francisco and State of California, have invented a certain new and useful Improvement in Concrete Roadways; and I do hereby declare the followin to be a full, clear, and exact description oi? the same,reference being bad to the accompanying drawings, forming a partof this eeification,and to the figures and letters 0 thereon.

This. invention relates to the nstruction of pavement for roadways and more espeelm? to that type wherein the surface is forim-d by a rock or stone aggregate ccm- [Til-"(l with an asphaltic binder which is substantially nonl-fi1id at ordinary temperatnres, but capable of being rendered limpid or liquid by best. he surface layer is usually supported by a suitable foundation, such as cement concrete; approved practice indicating the desirability of forming the surface of the base with pockets or irregu 1 larities as set forth. for instance, in my prior Patents Nos. 956,940, 965,562 and 9823.47, and the present invention will be described under the assumption that a foundation of the character stated, is emp oyed.

In so far as tln pa vement )roduced is concerned, it, is the ob ect of i ie invention to form a surface layer u liien will be a homogeneous mass, substantially free from voids and with such proportions o aggregate and binder as will aii'ord a maximum resistance. to wear and displar-enient nud'er iratlie conditions and at the same time conform to approved practice with respect to surfce conditions and res iency absorbing shock and vibration Without disintegration.

In so far as the process of producing the pavement is concerned. the objects of the invention are, to. reduce the number of steps and machinery necessary for handling and combin ng the ingredients; to bring the ingredients together in such inanner that the voids in the aggregate are tilled by capillary action from below, whereby the trapping of air or the formation of scaled cavities is prevented, and to ermit the use of a cheap and easily prepare or obtained aggregiite.

Attempts have been heretofore made .to produce a homogeneous layer of aggregate reference marked Serial No. 615,134. 7

and'asphaltic binder for roadway surfaces. For instance, it has been'proposed to grade the aggregate and to combine the graded material in certain proportions and sizes, and to mix the binder therewith bv agitation and heat, the completely mixed aggregate and binder being carried to and depos-' ited on the roadway where it is spread and ro led, but such operations do not. result in a homogeneous mixture, as the particles stick together, forming masses, some or all of which have larger proportions of certain sizes of the aggregate than others, and the binder is caused to drain out because of its hot liquid state, or to accumulate in larger per cent. in portions of the mass, where it, suddenly cools. W'hen laid and rolled not only is it impossible to prevent the leaving of a percentage of voids, but owing to the irregularity of the mixture, the surface layer will wear and disintegrate irregularly. It has also been proposed to pour a hot asphalt binder over a layer of aggregate, but owing to the rapid cooling of the binder, very irregular penetration results; furthermore, air is trapped in the layer of aggregate forming spaces or voids.

v inaccordance with the present invention, the inundation is prepared preferably of cementconcrete, and suitable provision at the top surface such as pockets or irregularities to retain the binder and bond the surface to the base more securely. Upon this-foundation there is spread alayer of binder cont' ning a large percentage of asphalt, said bmder being substantially non-fluid at ordinary temperatures, butcapable of being renderetl limpitl or fluid by heat. It is usually spread on the base while hot. enough to flow somewhat, but requires spreading to insure a uniform depth or distribution over the f -nuzlation. l

The aggregate with which the binder is m flm'nljlnt is POIHj' OSC'll of broken or natural- 12 the larger pieces of which are of less meter than the thickness of the layer of b they form a part. thus in a two inch er the larger sizes of the aggregate are referably such a will pass a three-fourth liE i-l or a one inch mesh. With this larger aggregate there is mixed it suliicient qr atity of sand or small size aggregate to surround the larger pieces. The surrmmding small size aggregate or sand should be Patented May 30, 1911.

.' Q I I 994,093

such that it has from to 4.0% voids, as it is within these limits that effective capillary action will operate to draw the binder u and cause the same to spread uniformly tirough the mass or layer of a greate. Should the percentage of vol 5 be arger, the interstices are too large to be filled, or'for capillarity to act eflectively, and should the percentage of voids be smaller the capillary action is blocked, probably because the finer particles float on or in the binder and close the passage ways or render the binder too viscid to feed by capillarity. The aggregate pref rably employed consists of 50% broken stone such as will pass a threequartcr or one inch mesh mixed dry with 50% sand having between 25% and 40% of voids. This aggregate is heated to a high temperature and distributed in an even layer over the layer of asphaltic binder; The layer of aggregate preferably approximates in thickness the thickness of the surface layer desired and the thickness of the layer of binder is such that ap roximately the whole of it will be absor ed by the heated aggregate. In other words. the'binder equals the void volume in the aggregate.

"The proportions to employ may be easily de l'errnincd for any given aggregate, for example .62 of an incli depth of binder will fill and be practically completely absorbed by a layer of aggregate containing 31% of voids when the aggregate is of a height or thickness of 2- inches, whereas. if the aggregate contains 40% of voids it should he only 1.55 inches thick for the same depth of binder. The practical result of the action of the hot aggregate on the binder is to render the latter limpidand in condition to feed by capillary action into the aggregate. This action takes place almost immediately, and although there is alarge volume of binder to be melted in proportion to the volume of cach of the finer particles of the aggregate, the stored heat due to the presence of the larger pieces of the aggregate is snllicient to effectively meltthe binder-and prevent the some from solidifying as it penetrates the mass of aggregate. The larger particles or pieces inthe aggregate, as just pointed out, perform an important function in the process, for without them thestorcd heat would be insufficient.

The limits within which the capillary action will be cil'ective in causing a normally non-fluid asphaltic binder to be effectively absorbed, it is believed is fairly well defined by the percentage of voids in the aggregate and to lie, as before stated, between 25% and 4.0%. To bring the percentage of voids within these limits, a. comparatively rough grading is all that is necessary with any crushed rock or gravel andthe addition of ordinary sand is usually sufficient to either reduce the percent-age of voids when too great or to increase the percentage of voids when too small.

The accompanying drawing shows a section of-a roadway and illustrates the process of layin the same.

In said rawing, A is the cement con crete base having pockets or irregularities B in its up er surface.

C is a ayer of normally non-fiuid as phaltic binder spread on the base to practirally uniform depth.

D is a hot layer of aggregate having approximately 50% of large particles 11 and 60% of smaller particles d, the latter having between and 40% of voids.

l) is a finished section in which the layer of binder has fed up by capillary action into the layer of aggregate so as to completely fill the voids therein.

After the binder has been melted and absorbed. and the layer is partly cool, the sur face is preferably smoothed and evened by rolling with a smooth roller.

Having thus described my invention, What I claim as new and desire to secure by Let lcrs Patent of the United States, is:

1. The method of pavement construction, 7

which consists in providing an aggregate composed of a mixture of wear resistant sionc'of such size as to have a large percent age of voids and sand or equivalent having a smaller percentage of voids. the interstices in the sand being of such size as to exert, capillary attraclirm on a limpid but normally non-fluid asphaltic binder. then heating the mixture of tone and sand and filling the interstices therein from the bottom by capillary action. with a normally noufluid asphallic binder rendered limpid bv the heat of the mixture of stone and son whereby a homogeneous layer is produced having no excess of either hinder or aggregate.

2. The method of pavement construction, which consists in spreading a body of asphaltic binder capable of being rendered limpid by heat on a suitable supporting foundation and in applying thereto a layer of heated aggregate having from to 40% of voids and containing a large proportion of relatively large size aggregate whereby the stored heat of the aggregate available for rendering limpid the necessary percentage of binder. to fill the voids by capillary action is increased.

3. The method of pavement construction, which consists in spreading a body of asphallic binder which is substantially noniluid at ordinary temperatures and in applying thereto a layer of heated aggregate having a percentage of voids substantially equal in volume to the volume of binder, the size of the interstices bet ween the particles of aggregate being within the limits of capillary attraction for the binder when rendered limpid by the hvatof the aggreof heated aggregate having not less than gate, whereby a' homogeneous layer of ag- 25%, nor more than 40% of voids, and Said gregate and binder is produced. voids being of a size to cause the binder 4. The method of pavement construction, when llmpld to penetrate the aggregate and 15 fill the voids by capillary action whereby a solid homogeneous layer is produced, and finally rollin g surface of the layer.

ED ARD M. GHADBOURNE.

which consists first in pro )aring a foundaticn impervious to nr-n-liuid binder, sec ondly, spreading on said foundation 3. layer of normally non-fluid binder containing a \VALTER M. Pm, Aux; C. DENISON.

10 being rendered Iimpid by hea t, thirdly,

large pcrceniagc of asphalt and capable of W'itnesses: spreading over said layer of binder a layer 1 

